1. Field of the Invention
The present invention relates to a light intensity measuring unit and a microscope including the light intensity measuring unit.
2. Description of the Related Art
In recent years, in the field of vital observation, fluorescent observation has been more and more important owing in part to diversified objects to be observed since practical application of fluorescent proteins such as GFP (Green Fluorescent Protein) and YFP (Yellow Fluorescent Protein).
In the fluorescent observation of a biological specimen, minimizing damage to the biological specimen is important. Irradiating the biological specimen with excitation light with an excessive intensity is undesirable. Furthermore, the light intensity per unit area of the excitation light impinging on the specimen needs to be determined to ensure the reproducibility and reliability of the observation.
In order to meet such a demand, various techniques to measure the intensity of excitation light or stimulation light (light quantity) impinging on a specimen have been proposed in the field of the microscopy.
Japanese Patent Laid-Open Publication No. 2007-93988 and Japanese Patent Laid-Open Publication No. 2007-183111 disclose a technique in which a branching optical element such as a beam splitter or a half mirror is arranged in an optical path for laser light so that part of laser light incident on the branching optical element can be guided to a photodetector, thus allowing the quantity of laser light impinging on a specimen to be determined based on the quantity of laser light detected by the photodetector.
Japanese Patent Laid-Open Publication No. 2005-352146 and Japanese Patent Laid-Open Publication No. 2005-91701 disclose a technique to measure the intensity of excitation light emitted from an objective, using a photodetector placed on a stage.